Electrolytic tin



Patented Mar. 18, 1924.

NITED sra'ras CLARENCE P. LINVILLE, OF ELIZABETH, NEW JERSEY, ASSIGNORTO AMERICAN SMELTING AND REFINING COMPANY, OF NEW YORK, N. Y., ACORPORATION OF NEW JERSEY.

No Drawing.

To all whom it may concern:

Be it known-that I, CLARENCE P. LIN- VILLE, a citizen of the UnitedStates, and resident of Elizabeth, in the county of Union and State ofNew Jersey, have invented certain new and useful Improvements inElectrolytic Tin, of which the following is a specification.

The invention'relates in general to a certain new and useful improvementin the production of electrolytically refined: tin from impure tinanodes and specifically relates to an additional agent for use in,-theelectrolyte in the electrolytic refiningof tin. The inventionconstitutes an improvement in the process defined in the patent to R. L.Vhitehead, No. 1,157,830, October 16,1915 and constitutes a companioncase with the applications of Harry, H. Alexander, Serial No. 434,124,and No. 434,114, on Electrolytic refining of tin, filed under even date.

Heretofore, as disclosed in the said patent to \Vhitehead and asdisclosed in the above identified applications, it is proposed toproduce from impure tin which usually contains lead, and otherimpurities, an electrolyte of such character that it will insure thecontinued maintenance of electrolytic decomposition of the tin duringthe refining operation. The Whitehead process consists fundamentally inmaintaining at least a six percent solution of tin in the electrolyteand in this condition the process can be operated continuously when theelectrolyte has in solution one-tenth of one per cent sulphuric acid andfifteen to twenty. per cent of hydrofluosi'licic acid; In the aboveidentified Alexander application it is proposed to in-, p

crease the sulphuric acid constituent and correspondingly decrease thehydroflu'osilicic acid constituent to meet certain conditions defined inthat application. With both of these hydrofiuosilicic-sulphuric acidelectrolytes it is found that under some conditions polarizations wouldoccur, the anodes would become insoluble presumably on account of theformation of hard slimes thereon and as a result the current wouldcontinue to plate tin out and the electrolyte would quickly becomedepleted of tin. ly out-growths are formed upon the cathodes causingshort circuits with resulting low ef- James Robert Stack, Serial Furtheroccasional ELECTROLYTIC TIN.

Application filed December 30, 1920. Serial No. 434,118.

ficiency. These growths were particularly prevalent in those situationswhere too much additional agents were present at the temperatureat whichthe process was practiced and it became a difficult problem to gauge theproper; amount of additional agents which should be added to theelectrolyte under the necessarily varying temperature conditionspresent. Accordingly, one of the objects of the invention is to rovidean, improved form of hydrofluosilicic-sulphuric acid electrolyte havingall of the virtues of this substance definedin the prior patentandapplications, above identified, and which at the same time willdefeat its tendency to form short circuiting sprouts or other polarizingaction.

I attain this object broadly by incorporating in the electrolyte eithera free halogen acid or a halogen salt capable of reacting with theelectrolyte to form the acid. Hy-

drochloric acid (HCl) is suggested as suit-' able but this is onlysuggestiveof one acid wh1ch has been found satisfactory under practicalworking conditions.

In a situation where there is an excess of sulphuric .acid, sodiumchloride (NaCl) or common salt may be added, in which case the reactionis presumably as follows:

In the case of theelectrolyte defined in the above identified patent andapplications it is found that the addition of two-tenths to three-tenthsper cent of hydrochloric acid or its equivalent in the electrolyte gavethe best results.

The presence of the sodium sulphate aparently has no effect upon theactivity of the electrolyte and the addition of the salt has an economicvalue over the use of the hydrochloric acid in that the salt is cheaper.In the method defined in the Alexander application there is an ampleexcess of sulphuric acid to unite with the small amount of salt presentto form the necessary amount of hydrochloric acid required by thisprocess.

It is further suggested to add both thesalt and the hydrochloric acid tothe electrolyte the halogens eliminates the formation of hard slimes andthus maintains the solubil-.

ity of the anode even in the presence of an excessive amount of additionagent and,

. even when the electrolyte is heated. The

anode corrosion is improved and a fine dense de ositis laid on thecathode.

aving thus described my invention, I claim: v

1.. An electrolyte for the deposition of tin free from lead, comprisingan electrolytic solution of tin in hydrofluosilicic acid containingsulphuric acid in an amount suflicient to react With the lead present toform an insoluble lead salt and to provide an excess of free sulphuricacid and an agent capable of reacting with said excess of sulphuric acidto form free hydrochloric acid.

2. In the electrolytic refining OfllUPUl'Q tin, the method of preventingcontamination of the tin deposited from the impure tin anode upon thecathode, which consists in employing as the electrolyte a solution oftin in hydrofluosilicic acid together with a quantity of sulphuric acidsuflicient to convert the lead of the dissolving anode into leadsulphate and a substance having chlorine radical and capable ofpreventing polarization. V

3., An electrolyte for the deposition of tin, free from lead, comprisingan electrolytic solution of tin, said solution includinghydrofiuosilicic acid an agent to protect the electrolyte from the leadpresent and a suitable soluble haloid salt.

4. An electrolyte for the depostion of tin, free from lead, comprisingan electrolytic solution of tin, said solution includinghydrofluosilicic acid, and an agent to protect the electrolyte from thelead present, in cluding ulphuric acid and a suitable soluble haloidsalt.

5. An electrolyte containing tin in solution, sulphuric acid and asoluble haloid salt said solution including hydrofluosilicic acid.

6. An electrolyte containing tin in solution and free hydrochloric acidsaid solution including hydrofluosilicic acid.

7. An electrolytic solution comprising hydrofluosilicic acid having tindissolved there-- in and including an agent to protect the solution fromthe action of any foreign material and including also a soluble haloidsalt.

8; An electrolytic solution comprisin hydrofluosilicic acid having tindissolved tierein and including sulphuric acid in an amount sullicientto react with any foreign material. 7

Signed at Perth Amboy in the county of Middlesex and State of New Jerseythis 10th day of December, A. D. 1920.

CLARENCE P. LINVILLE.

